or KISS/Meg fills - not sure about the Boris but IIRC the Meg is one of the larger scrubber capacities, so selling a container of 2 x that should keep everyone happy.
Another option would be some more reliable indication of scrubber usage - the current colour change products aren't held in great esteem round here.
The holy grail would of course be an easily packed, high CO2 capacity, low cost material... go on, you know you want to

Charlie, we have an easily packed, high CO2 capacity low cost material it is called sofnolime, go on you know you want to!!